1. Field of the Invention
The present invention relates to a high conductivity multilayer lead structure with a molybdenum layer for a read sensor and, more particularly, to a lead layer structure that has a molybdenum layer on a seed layer structure which provides conductivity nearly equivalent to a tantalum (Ta) and gold (Au) multilayer lead structure.
2. Description of the Related Art
The heart of a computer is an assembly that is referred to as a magnetic disk drive. The magnetic disk drive includes a rotating magnetic disk, a slider that has write and read heads, a suspension arm that supports the slider above the rotating disk and an actuator that swings the suspension arm to place the read and write heads over selected circular tracks on the rotating disk. The suspension arm biases the slider into contact with the surface of the disk when the disk is not rotating but, when the disk rotates, air is swirled by the rotating disk adjacent an air bearing surface (ABS) of the slider causing the slider to ride on an air bearing a slight distance from the surface of the rotating disk. When the slider rides on the air bearing the write and read heads are employed for writing magnetic impressions to and reading magnetic impressions from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
The write head includes a coil layer embedded in first, second and third insulation layers (insulation stack), the insulation stack being sandwiched between first and second pole piece layers. A gap is formed between the first and second pole piece layers by a nonmagnetic gap layer at an air bearing surface (ABS) of the write head. The pole piece layers are connected at a back gap. Current conducted to the coil layer induces a magnetic field into the pole pieces that fringes across the gap between the pole pieces at the ABS. The fringe field or the lack thereof writes information in tracks on moving media, such as in circular tracks on a rotating disk.
The read head includes a sensor that is located between nonmagnetic nonconductive first and second read gap layers and the first and second read gap layers are located between ferromagnetic first and second shield layers. In recent read heads a spin valve sensor is employed for sensing magnetic fields from the rotating magnetic disk. The sensor includes a nonmagnetic conductive layer, hereinafter referred to as a spacer layer, sandwiched between first and second ferromagnetic layers, hereinafter referred to as a pinned layer, and a free layer. First and second leads are connected to the spin valve sensor for conducting a sense current therethrough. The magnetization of the pinned layer is pinned perpendicular to an air bearing surface (ABS) of the head and the magnetic moment of the free layer is located parallel to the ABS but free to rotate in response to external magnetic fields. The magnetization of the pinned layer is typically pinned by exchange coupling with an antiferromagnetic layer.
The spin valve sensor is characterized by a magnetoresistive (MR) coefficient that is substantially higher than the MR coefficient of an anisotropic magnetoresistive (AMR) sensor. MR coefficient is dr/R were dr is the change in resistance of the spin valve sensor in response to signal fields and R is the resistance of the spin valve sensor before the change in resistance.
The read sensor, which may be a spin valve sensor or an AMR sensor, is bounded by a first edge at the ABS, a recessed edge spaced from the ABS and first and second side edges. First and second lead layers are connected to the first and second side edges respectively of the read sensor for the purpose of conducting the sense current therethrough. This type of connection is known in the art as a contiguous junction. Another type of connection is a continuous junction which is when the first and second lead layers overlap side portions of the read sensor layers with a space therebetween that defines the track width of the read head. It is important that the lead layers have low conductivity and be capable of withstanding operating temperatures in a magnetic disk drive which may be 80.degree. C.-120.degree. C. Low conductivity is important for minimizing heat and noise generated by the lead layers. If the lead layers have a high resistance they must be made thicker in order to reduce the heat and noise produced by the lead layers. Unfortunately, thicker lead layers increase the profile of the read head on each side of the sensor which is replicated in subsequent layers all the way to the write gap layer in the write head. This can cause write gap curvature which will cause the write head to write curved magnetic impressions into circular tracks on a rotating magnetic disk. This is undesirable since the read head reads straight across and will lose a portion of the signal at the outer edges of the magnetic impressions.
A typical material employed for lead layers is tantalum (Ta). While tantalum (Ta) operates well at operating temperatures it has a high resistance and suffers from the disadvantages described hereinabove. The resistance of a typical tantalum (Ta) lead layer can range from 2.2 to 2.8 ohms/sq. Gold (Au) is a desirable substitute for tantalum (Ta) because gold has a low resistance. A typical gold/nickel (Au/Ni) or gold/tantalum (Au/Ta) multilayer can have a resistance of about 1.0 ohms/sq. While such multilayers are very desirable from the standpoint of their conductivity, gold (Au) has not been able to withstand the aforementioned operating temperatures of the read head. The lead layers have edges at the ABS in the same manner as the layers that make up the read sensor. At operating temperatures the heat and attendant stresses cause the gold to ooze at the ABS like toothpaste. A contributing factor may be the expansion of layers in the read head which are adjacent the lead layers. Oozing of the gold at the ABS degrades the performance of the lead layers and can short the lead layers to the first and second shield layers, as well as shorting across edges of sensitive layers of the read sensor. Accordingly, there is a strong-felt need to provide lead layers that have a low resistance similar to gold but hard enough to withstand operating temperatures of the read head.